<div class="panel panel-default col-sm-4">
    <div class=" panel-body">
<?php
echo $this->Form->create('User', array('action' => 'login', 'class' => 'form-horizontal'));
echo $this->Html->div('form-group',
        $this->Form->label('usernamelabel', 'Username', array('class' => 'col-sm-4 control-label')) .
        $this->Html->div('col-sm-8', 
           $this->Form->text('username', array(
               'class' => 'form-control'
           )))
        );
echo $this->Html->div('form-group',
        $this->Form->label('passwordlabel', 'Password', array('class' => 'col-sm-4 control-label')) .
        $this->Html->div('col-sm-8', 
           $this->Form->text('password', array(
               'class' => 'form-control',
               'type' => 'password'
           )))
        );

echo $this->Html->div('form-group',
        $this->Html->div('col-sm-offset-4 col-sm-8',
        $this->Form->end('Login', array('class' => 'btn btn-default'))));
?>
    </div>
</div>